1. Field of the Invention
The present invention relates to a catalyst and a process for reverse disproportionation of ethylene and stilbene to produce styrene. The catalyst comprises tungsten, potassium, and iron on a silica support.
2. Description of the Prior Art
The production of styrene from stilbene and ethylene is disclosed in U.S. Pat. No. 3,965,206, the teachings of which are incorporated by reference. Use of conventional disproportionation catalysts such as cobalt molybdate on alumina, or tungsten oxide or silica, alumina or silica-alumina, for reverse disproportionation is taught.
U.S. Pat. No. 3,764,635, Fattore, et al, the teachings of which are incorporated by reference, teaches a process for disproportionating olefins using a catalyst of tungsten and bismuth on a support, preferably silica. The catalyst is active for disproportionation without any activation step.
U.S. Pat. No. 3,792,107, Fattore, et al, the teachings of which are incorporated by reference, discloses use of a catalyst of tungsten and copper or tungsten and Group VIII metals, preferably Fe, Co, or Ni, or silica or other support. It is claimed that this catalyst requires no activation before use in disproportionation.
U.S. Pat. No. 3,728,414, Helden, et al, the teachings of which are incorporated by reference, teaches a conventional olefin disproportionation catalyst with a promoter, a Group IIIa metal on an alumina carrier. Conventional olefin disproportionation catalysts are said to contain titanium, vanadium, chromium, manganese, zirconium, niobium, molybdenum, technetium, ruthenium, rhodium, palladium, tin, hafnium, tantalum, tungsten, rhenium, osmium, and iridium. This reference teaches that additional components, e.g., coactivators, hydrogenating components, components for isomerization of the double bond, and the like may also be added. Coactivators listed include cobalt oxide, and compounds of iron, nickel, and bismuth.
U.S. Pat. No. 4,192,961 teaches conversion of a mixture of dibenzyl and stilbene with ethylene in the presence of a catalyst of chromium oxide, tungsten oxide, an oxide of an alkali metal and silica or alumi-silicate. Styrene yields of 78 to 80 wt %, based upon conversion of ethylbenzene, dibenzyl and stilbene, are claimed.
U.S. Pat. No. 3,658,930, Kenton, et al, the teachings of which are incorporated by reference, teaches disproportionation of olefins using a rhodium oxide promoter on conventional olefin disproportionation catalyst, e.g., tungsten, molybdenum, rhenium, or tellurium on silica.
U.K. Patent specification No. 1,205,677 teaches disproportionation of olefins using a conventional catalyst, such as molybdenum trioxide, tungsten trioxide or rhenium heptoxide on alumina, silica, or alumina-silica, and incorporating into this conventional catalyst a second component to effect double bond isomerization of olefins. Group VIII noble metals are suggested as being suitble, with preferred isomerization catalysts containing platinum and especially palladium. An alkali or alkaline earth metal ions are added to the catalyst to serve as a base to inhibit the oligomerization of branched chain olefins.
None of these prior art catalysts are believed to possess sufficient activity and stability to permit their use in a commercial reverse disproportionation process.
Although it is desirable to have a catalyst which can be successfully reactivated at approximately the same temperature used for the reverse disproportionation reaction, the choice of a commercial catalyst must depend on other factors as well. A very significant factor is the cost of the catalyst. Same promoters, such as noble metals, are expensive.
Sometimes the increased productivity of a catalyst, which requires a high temperature activation more than justifies the increased costs associated with wear and tear on equipment and catalyst due to swings in temperature. Similarly, a longer cycle length, between regenerations is important in a commercial unit.
Use of iron, as a catalyst additive, significantly increases the ability of the catalyst to effect the reverse disproportionation reaction for extended periods of time, the iron slightly reduces productivity during the start of a run, but at the end of a 12-hour run the iron-promoted catalyst has a higher productivity than standard catalyst.